In the engagement the Bob Barker's bow was heavily dented in a collision with the harpoon ship, Yushin Maru No. 3, and another ship, the Steve Irwin, had its propeller temporarily entangled with ropes.

As further details of the confrontation emerged, the Japanese government said Sea Shepherd attackers in small boats had entangled the propeller of one of the fleet's three harpoon ships.

Advertisement

"The propeller of Yushin Maru No. 1 has been entangled with ropes," the Fisheries Agency of Japan said in a statement.

The FAJ said the vessel had no difficulty in navigation, but added: "The sabotage activities of the Sea Shepherd are acts of extreme danger which threaten the safety of Japanese research vessels and lives of their crew."

Mr Hammarstedt said after sustaining more than a dozen co-ordinated attacks on the Bob Barker by whaling ships trailing wire cables and rope, he launched two rigid inflatables to set up defensive positions as a last resort.

You will now receive updates fromBreaking News Alert

Breaking News Alert

"There is a big difference between having two RHIBs [Rigid Hull Inflatable Boats] trailing line in an act of self-defence and to deter further attacks - and another vessel towing 300 metres of steel cable across another vessels bow with the express intent of damaging the other vessel,” he said.

He said the Steve Irwin was currently being tailed by the whalers' security ship, Shonan Maru No. 2, but the third Sea Shepherd vessel, Sam Simon, was heading south free of pursuit after refuelling in New Zealand.

The group's Australian chairman, Bob Brown, called on the Australian and New Zealand governments to assert their authority by intervening.

"Instead we get the Abbott and key governments waggling their distant fingers at both sides and calling on everyone to take it easy," Dr Brown said.

"That's like the volunteer bushfire brigade coming across a mob of arsonists with flame-throwers, and the ministers calling on them to leave each other alone. "

Environment Minister Greg Hunt has said a second observation flight would be conducted by Customs officers aboard an Australian government Airbus A319.